1. Field of the Invention
The present invention relates to a variable displacement compressor for use in an automotive air-conditioning system and, more specifically, to a variable displacement wobble plate type compressor provided with a control valve, having a suction chamber, a discharge chamber, and a crankcase and capable of varying the stroke of the pistons thereof according to a difference between the crankcase pressure and suction pressure to vary the wobble angle of the wobble plate to control the compression displacement.
2. Description of the Related Art
A variable displacement compressor of a variable angle wobble plate type is disclosed in U.S. Pat. No. 4,428,718 granted to T. J. Skinner. In this compressor, when the suction pressure drops due to a drop in the cooling load or an increase in the rotating speed of the compressor, the bellows of a displacement control valve expand due to a variation of the balance between the discharge pressure and the atomospheric pressure, to operate the valve element and close an exhaust passage interconnecting the crankcase and the suction chamber, and to operate another valve element interlocked with the former valve element to open a supply passage interconnecting the discharge chamber and the crankcase, to increase the pressure difference between the fluid pressure in the crankcase chamber and the suction pressure by supplying a high pressure refrigerant gas into the crankcase chamber. The supply of the high pressure refrigerant gas into the crankcase increases the fluid pressure acting on the back face of each piston and shortens the stroke of each piston, to prevent a drop in the suction pressure of the compressor while decreasing the compressor displacement.
However, the above-mentioned conventional variable displacement compressor has a drawback in that, when the supply of the high pressure refrigerant gas from the discharge chamber to the crankcase chamber is interrupted during the operation of the compressor, the regrigerant gas is unable to immediately escape from the crankcase chamber to the suction chamber via the exhaust passageway. This is because the extent of opening of the exhaust passageway per se, i.e., the amount of restriction of the exhaust passageway, is constant and unchangeable. As a result, when the cooling load to the compressor is increased, the compressor is unable to quickly increase the compression displacement. That is, the response characteristics of the conventional variable displacement wobble plate type compressor are unsatisfactory during control of the compressor displacement in response to a change in the cooling load.